Project Summary Heart failure (HF) affects an expanding proportion of the population, and currently affects over 5 million adults in the United States alone. Due to chronic pressure overload of the left ventricle, tissue mechanics are permanently changed as interstitial fibrosis and hypertrophy of the myocardium occurs. Despite the prevalence of HF, there are no therapeutic strategies to reverse ? or even reduce ? cardiac fibrosis, aside from left ventricular assist devices and heart transplant, due to the poorly understood mechanobiological response of resident cardiac cells. During pressure overload induced HF, resident cardiac fibroblasts transition to activated myofibroblasts (MyoFBs), switching to the more contractile and hyper-secretory phenotype. MyoFBs express Talin1 (Tln1), a focal adhesion protein which activates integrins and undergoes force-induced mechanical unfolding, allowing for MyoFB attachment and transmission of force to and from the extracellular matrix (ECM). Preliminary data demonstrate that MyoFB Tln1 could be responsible for the adverse remodeling that occurs in HF, and deletion of this protein in MyoFBs during HF may improve cardiac function and decrease fibrosis. Thus, the central hypothesis of the current proposal is that MyoFB-specific deletion of Tln1 will reduce interstitial fibrosis, decrease left ventricular hypertrophy, and preserve cardiac function in the context of HF. We will first determine the ability of selective deletion of Tln1 from MyoFBs to reduce adverse remodeling of the surrounding myocardium in response to pressure overload (Aim1). Upon establishing Tln1 as a regulator of MyoFB mechanobiology and fibrosis, we will investigate the hypothesis that Tln1-mediated ECM deposition by MyoFBs contributes to altered cardiomyocyte (CM) hypertrophy during HF (Aim2). To study these aims, a novel MyoFB-specific Tln1 knockout mouse has been generated. Transverse aortic constriction (TAC) - an experimental model of pressure overload induced HF - will be performed, and echocardiography will be used to measure hemodynamic function of the mouse heart throughout the studies. Interstitial fibrosis and stiffness of the left ventricle will be characterized by picrosirius red staining and atomic force microscopy, respectively. CM hypertrophy will be characterized using wheat germ agglutinin staining. In vitro models will be employed to isolate the effects of ECM stiffness and ECM fibril thickness. CM and Tln1-/- MyoFB responses to these different mechanical stimuli will be investigated using traction force microscopy and micropipette aspiration. In summary, the results from this proposal will establish MyoFB Tln1 as a regulator of MyoFB-mediated cardiac fibrosis and CM hypertrophy and will highlight a novel therapeutic target for the treatment and management of HF.